Two U.S. senators who just returned from a brief trip to Iraq are calling on Iraqi leaders to do more to settle political differences and curb sectarian violence.

The top Republican and Democrat on the Senate Armed Services Committee are expressing frustration over what they describe as the Iraqi government's slow progress to forge political compromise, stem the violence and provide basic services to the Iraqi people.

The committee chairman, Republican Senator John Warner of Virginia, offered his bleakest assessment of Iraq to date. "To summarize it, it seems to me the situation is simply drifting sidewise," he said.

Warner says if the Iraqis do not make further progress toward stemming the violence by the end of the year, the U.S. Congress would have to make what he called bold decisions. He said all options would be considered, but did not elaborate further.

Senator Carl Levin, a Michigan Democrat, believes the Bush administration should set a timetable to begin a phased withdrawal of U.S. troops from Iraq to "force" the Iraqis to recognize that they must take more responsibility to change the situation in their country. "Unless they face up to the fact that they must make those political compromises, this is just going to be an endless quagmire for U.S. troops," he said.

But Senator Warner opposes setting a timeline for a U.S. troop withdrawal. "I am convinced we need to do everything we can to maintain the stability of this government, and put all pressure that we possibly can, recognizing that they are a sovereign nation, to get them to move forward more aggressively and do the job of a government; because if that government were to fail, if Iraq would devolve into a civil war, the consequences are frightful, not just for the Iraqi people, but for the whole region, and indeed for the whole world, because it would be viewed by the terrorists as a victory," he said.

Speaking at separate news conferences, Warner and Levin welcomed a new security plan announced by Prime Minister Nouri al-Maliki this week aimed at bringing together feuding Sunni and Shiite parties in his government to work jointly in local committees to stop the violence.

Senator Warner says the plan - details of which are yet to be hammered out - must be given a chance to work.

Warner and Levin were accompanied on the trip by Republican Senator Jeff Sessions of Alabama and Democratic Senator Mark Pryor of Arkansas.

Meanwhile, Senate Majority Leader Bill Frist of Tennessee completed his own trip to Iraq this week.

Frist, a heart surgeon, met with Iraqi doctors in Baghdad, as well as U.S. troops and government officials.

The lawmakers' visits to Iraq come just five weeks before midterm elections and amid continued concern among the American people about the U.S. military effort in Iraq.

A new public opinion poll by the Pew Research Center finds that 58 percent of Americans believe the U.S. mission in Iraq is not going well, while 47 percent say the war is hurting, not helping, the fight against terrorism.

Democrats hope the unpopularity of the war will translate into votes for them on November 7, and perhaps return control of Congress to their party.